It looks to me like Wacom has a special mount and not a Vesa mount.

This display mount works with the standard Vesa mount.


For your setup to work you would need something like this in addition:
Wacom VESA Mount for Cintiq 24 & 32

Finally, you need to add the weight of the display and the additional mount. If this is totally under the described maximum load, everything should work! :)